#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<math.h>

int main()
{
	double Xa, Xb, Ya, Yb;
	double len;
	scanf("%lf%lf", &Xa, &Ya);
	scanf("%lf%lf", &Xb, &Yb);
	len = sqrt((Xa - Xb) * (Xa - Xb) + (Ya - Yb) * (Ya - Yb));
	printf("%.3f\n", len);
	return 0;
}